class UnionFind():
  def __init__(self, n):
    self.n = n
    self.parents = [-1] * n

  def find(self, x):
    if self.parents[x] < 0:
      return x
    else:
      self.parents[x] = self.find(self.parents[x])
    return self.parents[x]

  def union(self, x, y):
    x = self.find(x)
    y = self.find(y)

    if x == y:
      return

    if self.parents[x] > self.parents[y]:
      x, y = y, x

    self.parents[x] += self.parents[y]
    self.parents[y] = x

  def same(self, x, y):
    return self.find(x) == self.find(y)

  def roots(self):
    return [i for i, x in enumerate(self.parents) if x < 0]

  def members(self, x):
    root = self.find(x)
    return [i for i in range(self.n) if self.find(i) == root]

  def size(self,x):
    return abs(self.parents[self.find(x)])

  def groups(self):
    roots = self.roots()
    r_to_g = {}
    for i, r in enumerate(roots):
      r_to_g[r] = i
    groups = [[] for _ in roots]
    for i in range(self.n):
      groups[r_to_g[self.find(i)]].append(i)
    return groups

N, M = map(int, input().split())
setlis = [set() for _ in range(N)]
for i in range(N):
  b,c = map(int, input().split())
  setlis[c-1].add(b-1)
uf = UnionFind(M)
ans = 0
for i in range(N):
  lis = list(setlis[i])
  if not len(lis): continue
  a = lis[0]
  for l in lis[1:]:
    if not uf.same(a,l):
      ans += 1
      uf.union(a,l)
print(ans)